I THE ATOMIC WEIGHTS. 



These figures, rather roughly determined, and by no 

 means exact enough to meet the requirements of modern 

 science, give a mean vakie of 16.021 for the atomic weight 

 of oxygen. As the weighings were not reduced to a vacuum, 

 this correction was afterwards applied by Clark,* who showed 

 that these syntheses really make O = 15.894; or, in Ber- 

 zelian terms, if = 100, H = 12.583. 



In 1842 Dumasf published his elaborate investigation 

 upon the composition of water. The first point was to get 

 pure hydrogen. This gas, evolved from zinc and sulphuric 

 acid, might contain oxides of nitrogen, sulphur dioxide, 

 hydrosulphuric acid, and arsenic hydride. These impuri- 

 ties were removed in a series of wash bottles ; the HgS by a 

 solution of lead nitrate, the HgAs by silver sulphate, and 

 the others by caustic potash. Finall}^ the gas was dried by 

 passing through sulphuric acid, or, in some of the experi- 

 ments, over phosphorus pentoxide. The copper oxide was 

 thoroughly dried, and the bulb containing it was weighed. 

 By a current of dry hydrogen all the air was expelled from 

 the apparatus, and then, for ten or twelve hours, the oxide 

 of copper was heated to dull redness in a constant stream of 

 the gas. The reduced copper was allowed to cool in an 

 atmosphere of hydrogen. The weighings were made with 

 the bulbs exhausted of air. The following table gives the 

 results : 



Column A contains the symbol of the drying substance. 

 B gives the weight of the bulb and copper oxide. C, the 

 weight of bulb and reduced copper. D, the weight of the 

 vessel used for collecting the water. E, the same, plus the 

 water. F, the weight of oxygen. G, the weight of water 

 formed. H, the crude equivalent of H when = 10,000. 

 I, the equivalent of H, corrected for the air contained in the 

 sulphuric acid employed. This correction is not explained, 

 and seems to be questionable. 



* Philosophical Magazine, 3d series, 20, 341. 

 f Compt. Rend., 14, 537. 



